Shadow mask and process for manufacture

ABSTRACT

A shadow mask for a color television picture tube has a domeshaped face and a skirt extending in a plane substantially parallel to an axis between the center of the electron guns of the tube and the center of the dome-shaped face. The skirt has a plurality of ribs and each of the ribs extends from the domeshaped face preferably parallel to the aforementioned axis. The process for making the shadow mask allows formation of the domeshaped face, the skirt, and the ribs in one single-stroke stamping operation. Beginning with a mask flat having an apertured area and a border, the process generally comprises the steps of dishing the dome-shaped face into the apertured area and a portion of the border adjacent the apertured area and simultaneously drawing the skirt and a plurality of ribs in the skirt from the remaining portion of the border.

United States Patent [191 Snook et al.

[ Dec. 17, 1974 SHADOW MASK AND PROCESS FOR MANUFACTURE [73] Assignee: General Electric Company, 7

Syracuse, NY.

22 Filed: on. 12, 1973 21 Appl. No.2 405,845

Related U.S. Application Data [63] Continuation-impart of Ser. No. 302,071, Oct. 30,

I972, abandoned.

[52] U.S. Cl. 313/402, 313/348 [51] Int. Cl. l-l0lj 29/06 [58] Field of Search 313/85 S, 92 B, 348

[56] References Cited UNITED STATES PATENTS 2,795,718 6/1957 Hekken et a1. 313/92 B 3,351,996 ll/l967 Fiore 3l3/85 S 3,585,431 6/l97l Long 3l3/85 S Primary Examiner-James W. Lawrence Assistant ExaminerWm. H. Punter Attorney, Agent, or Firm-Marvin Snyder [5 7 ABSTRACT A shadow mask for a color television picture tube has a dome-shaped face and a skirt extending in a plane substantially parallel to an axis between the center of the electron guns of the tube and the center of the dome-shaped face. The skirt has a plurality of ribs and each of the ribs extends from the dome-shaped face preferably parallel to the aforementioned axis. The process for making the shadow mask allows formation of the dome-shaped face, the skirt, and the ribs in one single-stroke stamping operation. Beginning with a mask flat having an apertured area and a border, the process generally comprises the steps of dishing the dome-shaped face into the apertured area and a portion of the border adjacent the apertured area and simultaneously drawing the skirt and a plurality of ribs in the skirt from the remaining portion of the border.

8 Claims, 21 Drawing Figures PATENTED 1 71974 3. 855.493

sum 1 OF 9 28B 22 F|G.3

PATENTED 55131 71974 FIG. 6

FIG.7 46

SHADOW MASK AND PROCESS FOR MANUFACTURE This application is a continuation-in-part of our copending application Ser. No. 302,071, filed Oct. 30, 1972, now abandoned and relates to an improved shadow mask for a color television picture tube and process for making the mask; more particularly, the invention relates to that type of shadow mask having a skirt with a plurality of ribs in the skirt.

A shadow mask for a color television picture tube comprises a piece of metal having a plurality of very small apertures aligned in predetermined positions in a specific number of horizontal rows. The shadow mask fits internally behind the viewing surface of the picture tube. An electron beam composed of electrons emanatin g from one or several electron guns scans horizontally across the shadow mask. The axis between the center of the electron guns in the picture tube and the center of the apertured portion of the mask mounted in the tube is known in the art as the Z axis. This axis is normal to the plane of the incremental area where it meets the mask.

When the electron beam passes through each aperture a predetermined one of the red, blue or green phosphor dots deposited on the interior side of the picture tube viewing screen is illuminated. The shadow mask serves to block any stray electrons in the electron beam from illuminating any phosphor dot other than the intended dot. Thus, the position of the shadow mask and the position and size of the apertures in relation to the phosphor dots is critical; any misalignment or change in position between the shadow mask and the phosphor dots or any change in the aperture size will cause undesired dots or combinations of dots to be illuminated, thereby causing improper colors to be observed by the viewer.

To properly perform its function, the shadow mask sign positions in the shadow mask, and have no apertures pulled or elongated from their predetermined sizes.

Shadow masks are conventionally formed from a flat piece of metal known as a mask'flat which has an apertured area and a border. The apertured area and a minor portion of the border adjacent the apertured area are dished, or pressed into a dome-shaped face of curvature somewhat similar to the curvature of the inside surface of the picture tube viewing screen. The remainder or major portion of the border is then drawn through a die or bent to form a skirt which surrounds the dome-shaped face and extends substantially parallel to the Z axis. The skirt reinforces the dome-shaped face, gives it predicatable rigidity necessary for proper alignment under various thermal conditions, and serves as a means for connecting the shadow mask to a frame. The frame retains the shadow mask and, in turn is joined to the interior of the picture tube.

Conventional shadow masks and processes for making them have exhibited various structural problems. Early prior art shadow masks had narrow skirts less than one inch wide, and consequently required heavy frames to properly retain the dome-shaped face. The weight of these shadow masks created problems resulting fromhandling and moving the picture tube since a substantial shock or jar could dislodge the shadow mask from its critical design position. For this reason lightweight shadow masks having wider skirts and lightweight frames have been used. The larger skirt, which may exceed 2 inches in width, is employed to compensate for the less massive frame and to add rigidity to the lightweight shadow mask.

Forming lightweight shadow masks having larger skirts has heretofore been difficult due to the large amount of the mask flat border which must be drawn through a die to form the skirt. Substantial force is exerted on the mask flat as the skirt is being drawn which, in the prior art, often resulted in stretching of the material in the apertured areas of the shadow mask, especially in the comers where the flat border must be stretched and condensed into rounded surfaces. This stretching causes a number of undesirable effects: the apertures are pulled into elongated ovals thereby increasing their size and allowing the electron beam to strike undesired phosphor dots; the apertures are pulled out of position and alignment so that they are displaced from their design locations; and the domeshaped face shows a tendency to be distorted out of the desired curved shape, thereby causing the distorted portions to be outside the critical positional tolerance allowed from the inside of the picture tube viewing surface.

In addition to the longer skirts, reinforcing ribs have been formed in the skirts to increase the rigidity of the lightweight shadow masks. Prior art processes for producing these reinforcing ribs have exhibited substantial disadvantages. These processes have generally required two separate stamping operations; one stamping operation to form the mask flat into the dome-shaped face and skirt and a second stamping operation to form the reinforcing ribs. A disadvantage of the two-step process is that the second stamping operation to form the ribs tends to cause so-called soft spots in the dome-shaped face. Soft spots result when the metal in a particular area is under a different mechanical stress than the surrounding areas and occur when the shape of the metal is altered after having once been formed, which is precisely what occurs in a second rib-forming operation. Soft spots are undesirable because they expand or contract more than the evenly stressed areas as the shadow mask is warmed by repeated scanning of the electron beam, resulting in an attendant distortion of the soft spot areas out of the critical positional tolerance limit. Another disadvantage of the second stamping operation is that distortions are easily induced in the domeshaped face as a result of the extreme difficulty in properly aligning and retaining the shadow mask after the first stamping operation in its formation. The springback characteristics of the metal cause this retention problem, making it almost impossible to add the ribs in a second operation without inducing distortions.

Further disadvantages of prior art lightweight shadow masks result from the design configuration of the ribs themselves. As previously stated, stretching and condensing the flat metal into a rounded surface such as a corner has heretofore caused great problems in shadow masks. Prior art configurations are not designed for the purpose of gathering or pulling excess metal from these rounded surfaces to make the fonnation process easier and to eliminate the previously described undesirable effects. Indeed, some prior art rib configurations utilize a construction which prevents gathering the excess metal. Further, prior art rib configurations have caused the skirt to bow outward from the most desirable position which would facilitate its assembly to the frame.

The present invention overcomes the foregoing problems by providing a shadow mask having ribs of advantageous size and configuration, and by providing one single-stroke stamping operation for forming the shadow mask including the ribs. Elongation and misalignment of the apertures, together with any distortion of the dome-shaped face, are prevented by securely gripping the mask flat during the forming process. Soft spots and distortions in the dome-shaped face are eliminated because the single-stroke stamping operation dis tributes forces to prevent formation of areas of uneven stress. Additionally, new and useful ribs are provided to eliminate undesirable gathering of metal wrinkles in the corners and to facilitate assembly of the shadow mask to the frame.

One object of this invention is to provide a new and useful process for forming a shadow mask having a dome-shaped face, a skirt, and a plurality of ribs in the skirt in one single-stroke stamping operation.

Another object of this invention is to provide a new and useful process for forming a shadow mask which prevents distortion and occurrence of soft spots in the dome-shaped face.

Another object of this invention is to provide a new and useful process for forming a shadow mask which avoids elongating the apertures and pulling the apertures out of alignment.

Still another object of this invention is to provide a new and improved shadow mask of the type having ribs to reinforce the shadow mask and to gather excess metal from the curved areas.

A further object of this invention is to provide a shadow mask that is capable of being formed in one single-stroke stamping operation and is inexpensive to manufacture, sufficiently rigid, easy to assemble to a frame, and light in weight.-

To achieve the foregoing and other objects, the process for forming the shadow mask begins with a mask flat having an apertured area and a border. The process comprises the steps of dishing a dome-shaped face into 7 the apertured area and a portion of the border adjacent the apertured area, and drawing a skirt and a plurality of ribs therein from the remaining portion of the border.

The shadow mask produced by the process of the invention comprises a dome-shaped face, a skirt extending from the periphery of the dome-shaped face in a direction substantially parallel to the Z axis, and a plurality of ribs formed in the skirt with each of the ribs extending longitudinally in a direction preferably parallel to the Z axis.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the invention may be had by referring to the accompanying detailed description and drawings in which:

FIG. I is a perspective view of a preferred embodiment of the shadow mask comprising a part of the present invention;

FIG. 2 is a top view of a mask flat from which the shadow mask is formed;

FIG. 3 is a top view of the shadow mask of FIG. 1;

FIG. 4 is an illustration of the mask of FIG. 3 as viewed in the direction of arrows 4-4 in FIG. 3;

FIG. 5 is a side view of a frame to which the shadow mask may be attached;

FIG. 6 is a perspective view of the major components of a die used in the process of forming the shadow mask;

FIG. 7 is a sectional view of FIG. 6 taken along lines 77 of FIG. 6;

FIGS. 8A through 8F are partial views of some of the components of FIG. 7, to illustrate the various steps in the process of forming the shadow mask,

FIGS. 9A and 9B are longitudinal views of alternative rib configurations;

FIGS. 10A, 10B and 10C are cross-sectional views of alternative rib configurations;

FIG. 11 is a top view of an alternative rib configuration; and

FIGS. 12A and 12B are broken away views of elements of the die which exemplify modifications that may be employed to form some of the rib configuratrons.

DETAILED DESCRIPTION OF THE INVENTION One embodiment of the shadow mask comprising the present invention is illustrated in FIG. 1. The shadow mask includes a dome-shaped face 20 and a skirt 22 which extends from the periphery of the dome-shaped face in a direction substantially parallel to the Z axis. The dome-shaped face is a curved surface which corresponds to the inside surface of a color television picture tube viewing screen. Formed in skirt 22 are a plurality of ribs, a few of the ribs being individually referenced at 24. Each of the ribs extends longitudinally from the dome-shaped face 20, and away from skirt 22 by no more than 0.025 inch. Inthe preferred embodiment, the ribs protrude outward from the skirt and are substantially parallel to the Z axis.

The shadow mask of FIG. 1 is formed from a flat piece of metal known as a mask flat. A mask flat 25 is shown, in FIG. 2, as comprising an apertured area 26 and a solid metal border 28. The mask flat typically is approximately 0.006 inch thick. The-apertures making up the apertured area are produced by well-known etching methods and are designed to have a predetermined positional alignment in a specific number of rows.

FIG. 3 illustrates all of the dome-shaped face 20 which is formed from the apertured area 26 and a minor portion 28A of the border 28 adjacent the apertured area. The minor portion 28A and a remaining portion 285 of border 28 are illustrated in FIG. 2. The remaining major portion 283 of the border forms the skirt 22 and the plurality of ribs 24 formed therein, as can be seen in FIG. 3.

The curved surface of dome-shaped face 20 is best illustrated in FIG. 4,'which depicts the mask of FIG. 3 as viewed along line 4-4 in the direction of the arrows. In FIG. 4, skirt 22 is seen as extending substantially parallel to the Z axis, with the same reference numerals designating corresponding parts shown in FIGS. 1, 2 and 3. Ribs 24 are shown in a preferred form extending substantially parallel to the Z axis.

A rigid metal frame 19 is shown in FIG. 5. The frame is attached, generally by spot welding, to the interior of the skirt 22 with the surface of the frame opposite the dome-shaped face protruding slightly beyond the outer tate assembly of the frame to the shadow mask. The ribs eliminate the tendency of the shadow mask to bow inwardly or outwardly and thereby allow the frame to be easily inserted inside the skirt. The frame is subsequently fastened within the picture tube by use of clips (not shown) on the frame that attach to studs in the picture tube.

The amount of excess metal gathered is dependent upon the number and size of the ribs in the mask assembly, for any given tube size. For example, in a 19 inch tube, the long side of the unformed mask flat, measured between points 29L of mask flat 25 illustrated in FIG. 2, is 14.500 inches; however, when the mask has been formed from the flat, the distance between the same points is 13.750 inches. This leaves 0.750 inch of material to be gathered on the long side of the mask. Each rib protruding outward from the mask skirt by 0.025 inch gathers 0.050 inch of material, since each side of the rib accounts for 0.025 inch of gathered material. Thus fifteen ribs on the long side of the mask gather the necessary 0.750 inch of material. Similarly, the short side of the unformed mask, measured between points 298 of mask flat 25 illustrated in FIG. 2 is 10.1875 inches; however, when the mask has been formed from the flat, the distance between the same points is 9.7500 inches, leaving 0.4375 inch of material to be gathered on the short side of the mask. Since each rib protruding outward from the mask skirt by 0.025 inch gathers 0.050 inch of material, nine ribs on the short side of the mask gather 0.0125 inch more than the necessary amount, which allows use of ribs protruding outward from the mask skirt by somewhat less than 0.025 inch. As an alternative, ribs protruding by 0.005 inch on a mask skirt for a 19 inch tube must number 75 on the long side and 44 on the short side in order to form the mask skirt without accumulating excess material at its corners and thereby permit the mask skirt to fit over the frame without distorting the mask.

The distance by which the ribs protrude from the skirt, in order to implement the teachings of the instant invention, is preferably less than 0.025 inch. Theoretically, the smaller the protrusion of each rib, and the greater the number of ribs, the better the gathering of metal. A practical range of rib sizes is'0.005 0.015 inch, with a maximum being 0.025 inch. Above 0.025 inch, an excessive amount of material must be drawn sideways between the ribs in order to permit excess material from the corners of the mask to flow into the ribs; consequently, the ribs are unable to gather the entire amount of such excess material, thereupon causing some buckling of the mask skirt at its corners.

The shadow mask of the instant invention is formed in a single operation by use of a press and a die. FIG. 6 generally illustrates a portion of a typical press and a die that may be used to practice the mask forming process. Since operation of a die is well known, the description herein is limited to the basic elements and movements required to understand the process. The press includes an upper platen 32 and a lower platen 34, which are movable with respect to each other. Typically the upper platen is movable while the lower platen may-remain stationary. Attached to upper platen 32 is an upper die shoe 36, and affixed rigidly to upper die shoe 36 is a punch 38. Movably mounted to upper die shoe 36 is an upper draw ring 40 surrounding, and shown extending beneath, punch 38. Attached to lower platen 34 is a lower die shoe 42, and movably attached to lower die shoe 42 are a trap pad 44 and a lower draw ring 46 surrounding trap pad 44.

FIG. 7 is a sectional view taken along each of the dashed lines 77 in FIG. 6, wherein like reference numerals indicate like elements, and showing additional elements to aid in explanation of the process of forming the shadow mask. Upper draw ring 40 is movably attached to upper die shoe 36 by means of a number of upper piston assemblies 50. These piston assemblies function in a manner similar to dashpots having pressure regulated retarding action. Through an oil feed and pressure regulation system (not shown), oil is forced into an expandable chamber forming part of the piston assemblies 50 for the purpose of extending upper draw ring 40 from upper die shoe 36. When upward force is exerted on the upper draw ring tending to push it toward the upper die shoe, the pressure regulator assembly prevents any significant retraction of the upper die shoe from its extended position until the pressure experienced by the oil exceeds a predetermined pressure limit, at which time oil is allowed to escape from the piston assembly with a constant pressure. Thus the oil feed and pressure regulation system allows upper draw ring 40 to retract relative to upper die shoe 36 and punch 38 under a condition of constant pressure or force.

Lower piston assemblies 52 are similar in operation and function to the upper piston assemblies 50. Oil forced into the expandable chambers of the piston assemblies 52 extends trap pad 44 from lower die shoe 42. Support pins 54 require lower draw ring 46 to move simultaneously with trap pad 44 except when the lower draw ring contacts a shoulder 56 of lower die shoe 42 during downward movement. Thus, a downward force on trap pad 44 and lower draw ring 46 causes no significant movement until the pressure limit forthe lower piston assemblies 52 is exceeded, thereby allowing the trap pad and the lower draw ring to move downward under constant pressure. Downward movement continues until the lower draw ring is stopped by the lower die shoe shoulder 56. At this point the support pins 54 no longer support the lower draw ring, and only the trap pad 44 is forced to move further downward under the regulated pressure.

Separator pins 58 rest on lower die shoe shoulder 56 through openings in lower draw ring 46 so that the lower draw ring is free to move relative to these pins.

The separator pins 58 stop the downward movement of the upper draw ring 40 at a certain point in the process.

Preliminary to formation of the shadow mask, the mask flat 25, previously described in conjunction with FIG. 2, is annealed. Annealing produces the desired mechanical, physical, and other properties by reducing hardness of the metal, improving its workability, and facilitating its cold working. Following annealing, the mask flat is subjected to roller-leveling which includes sending the mask flat through a tortuous path between a number of rollers in order to accomplish grain breaking, or breaking of the metallic grain orientation and structure, to help prevent the mask flat from being distorted or damaged when it is drawn and formed. Annealing and grain breaking are well known in the art.

The process of forming a ribbed shadow mask may be understood with the aid of FIGS. 8A through 8F which are partial views of the apparatus of FIG. 7. The dashdot lines in FIGS. 8A through 8F represent the position of the various elements prior to the position shown by solid lines. The distance between the solid and dash-dot lines represents the movement of these elements from the previous step to the step indicated by the solid lines. In FIGS. 88 through 8F the mask flat of FIG. 2 has not been shown in order to clearly illustrate the steps of the process, but it should be understood that the mask flat remains in the die until completion of the shadow mask forming process.

Formation of the shadow mask in one single-stroke stamping operation is begun by placing the mask flat 25 in a proper location on trap pad 44 and lower draw ring 46. Upper platen 32 and its attached parts, as shown in FIG. 7, are advanced until upper draw ring 40 initially contacts mask flat 25. This is illustrated in FIG. 8A.

A major portion of the border of the mask flat is gripped when the die is positioned as shown in FIG. 8B. This is accomplished by advancing upper platen 32, shown in FIG. 7, causing upper draw ring 40 to force the mask flat downward, thereby also tending to force the lower draw ring 46 down slightly, as shown in FIG. 8B. The lower piston assemblies, shown in FIG. 7, restrain the downward movement of trap pad 44 caused by force transmitted through support pins 54 from lower draw ring 46. Thus, the mask flat is tightly gripped at the major portion 28B of its border 28 between upper draw ring 40 and lower draw ring 46.

Downward movement of upper platen 32 causes the oil pressure in the upper piston assemblies 50 to increase until the upper pressure limit is exceeded, at which time movementof upper draw ring 40, lower draw ring 46, and trap pad 44 is halted. Punch 38, how ever, continues to move relative to these elements, and a dome-shaped face is thereby dished into apertured area 26 and a minor portion 28A of the mask flat border 28 when the die is positioned as illustrated in FIG. 8C. The dome-shaped face results from forcing the mask flat to conform to the curvature of punch 38 and trap pad 44.

The dome-shaped face is thereafter gripped as the die advances to the position shown in FIG. 8D. The gripping occurs as punch 38 progresses from its position shown in FIG. 8C and forces the mask flat against trap pad 44 while hydraulic pressure in the lower piston assemblies 52, shown in FIG. 7, restrains the trap pad movement. When the dome-shaped face is gripped, the downward force caused by punch 38 exceeds the downward force caused by upper piston assemblies 50 on upper draw ring 40, so that lower piston assemblies 52 experience a pressure greater than that caused by upper piston assemblies 50. This pressure differential forces upper draw ring 40 downward, and trap pad 44 and lower draw ring 46 begin to move downward under the force of the punch 38. The upper piston assemblies, being pressure regulated, continue to create a downward force on upper draw ring 40 so that it follows the downward movement of lower draw ring 46 until it is stopped by the separator pins 58. This is the condition illustrated in FIG. 8D.

The major portion 28B of border 28 is next released, under the condition illustrated in FIG. 8E. While upper draw ring 40 is prevented from moving downward beyond its position shown in FIG. 8D by separator pins 58, punch 38 continues to press against the domeshaped face to force trap pad 44 downwardly against the pressure regulated lower piston assemblies. The lower draw ring 46 follows trap pad 44 until it comes to rest on lower die shoe shoulder 56, at which time further movement of lower draw ring 46 is stopped. Because of the restrained position of upper draw ring 40 on separator pins 58 and the resting position of lower draw ring 46 on lower die shoulder 56, a gap greater than the thickness of the mask flat occurs between the surfaces of the upper and lower draw rings, thereby releasing major portion 28B of the border. This condition is depicted in FIG. 8E. The releasing action may occur contemporaneously with the gripping of the domeshaped face at some time after initial contact of upper draw ring 40 with separator pins 58 and prior to initial contact of lower draw ring 46 with lower die shoe shoulder 56.

The step of simultaneously drawing a skirt and a plurality of ribs therein in major portion 28B of the border is fully completed when the condition illustrated in FIG. 8F has been reached. This step occurs when punch 38 continues to advance from its position shown in FIG. 8E while the dome-shaped face is gripped between the punch and trap pad 44, thereby drawing the major portion of the border over the edges of draw ring 46. By drawing the major portion of the border over draw ring 46, the metal is forced to flow into a plurality of grooves 60 on the inside surface of lower draw ring 46. Grooves 60 form the ribs in the skirt, and space 62 between punch 38 and lower draw ring 46 forms the portions of the skirt between the ribs. Since the ribs are formed simultaneously with the skirt and the metal gathering action caused by formation of the ribs also occurs simultaneously with formation of the skirt, less stress is exerted on the corners of the apertured area. This reduced stress prevents the elongation of the apertures that would result in absence of the metal gathering action of the ribs.

At this juncture the process is complete and the shadow mask has been formed by a single stroke of the die. The die is reversed and all the elements thereof are returned to their initial position as shown in FIG. 7 preparatory to formation of another shadow mask in a similar single-stroke stamping operation.

The configuration of the individual ribs 24 may vary according to design requirements of those skilled in the art. One important consideration in these requirements is the amount of metal desired to be gathered from the corners of the shadow mask in order to facilitate formation of the rounded surfaces at the corners. Accordingly, a variety of different rib configurations may be required.

FIG. 9A shows a longitudinal view of one configuration of a rib 24 protruding at a substantially constant distance of no more than 0.025 inch from a region 64 of skirt 22 adjacent dome-shaped face 20 to an outer edge of the skirt. The width of this rib, measured in the plane of the skirt, may be constant or, in the alternative, may increase with distance from the dome-shaped face of the mask. FIG. 9B shows a longitudinal view of another configuration of a rib 24 protruding at a distance which increases from a region 64 of skirt 22 adjacent dome-shaped face 20 to no more than 0.025 inch at an outer edge of the skirt. The width of the rib in this embodiment also, measured in the plane of the skirt, may be constant or, in the alternative, may increase with distance from the dome-shaped m'ask face.

Different cross-sectional configurations for rib 24 are possible, as shown in FIGS. 10A through 10C. FIG. 10A illustrates a substantially rectangular crosssectional configuration, FIG. 10B depicts a substantially triangular cross-sectional configuration, and FIG. 10C shows a substantially semicircular cross-sectional configuration. In each instance, the rib protrudes no more than 0.025 inch from the skirt. However, the width of these cross-sections at the top may increase with distance from the dome-shaped face of the mask, as shown in top view in FIG. 11 for rib 24 on skirt 22.

To form some of the rib configurations previously discussed, protrusions on punch 38 of FIG. 7 complementing grooves 60 in lower draw ring 46 may be employed. For example, FIG. 12A shows a side view of a protrusion 68 on punch 38 and a complementing groove 70' on lower draw ring 46 used in forming the rib having the configuration shown in FIG. 9B. A further example in FIG. 128 shows a top view of a protrusion 68 on punch 38 and a complementing groove 70" on lower draw ring 46 used in forming the rib having the configuration shown in FIG. 10A. Other rib configurations may not require protrusions on the punch. For example, ribs having constant protrusion height and semicircular cross-sections have been formed with no protrusion on the punch but with semicircular grooves of constant depth in lower draw ring 46.

It will be understood by those skilled in the art that essentially any cross-sectional configuration of rib may be combined with essentially any longitudinal configuration, depending upon design requirements. Likewise, many of the parameters of the die previously described may be varied as desired by those skilled in the art. For

example, it has been found that shadow masks for 19V and V color television picture tubes are best formed if the number of upper piston assemblies used to restrain the upper draw ring is equal to the number of lower piston assemblies used to restrain the trap pad and the lower draw ring. Each of the piston assemblies used are preferably of the same size, and the pressure limit of each piston in the upper piston assemblies is set at a lower value than the pressure limit of each piston in the lower piston assemblies.

The foregoing specification has provided a detailed description of the process for forming a shadow mask in one single-stroke stamping operation, as well as a description of the shadow mask formed by the process.

Although specific embodiments of the invention have been shown and described, those skilled in the art will perceive changes and modifications that can be made without departing from the invention, and it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A shadow mask adapted to be mounted within a color television picture tube having a plurality of electron guns therein such that a Z axis extending between the center of the electron guns and the center of said mask is oriented normal to the plane of the incremental area of said mask where said axis intersects said mask, said mask comprising:

a dome-shaped face;

a skirt extending from the periphery of the domeshaped face substantially parallel to said Z axis; and

a plurality of ribs formed in said skirt, each of said ribs extending longitudinally along the general direction of the Z axis and extending away from said skirt by no more than 0.025 inch.

2. The shadow mask recited in claim 1 wherein each of said ribs extends substantially parallel to said Z axis and protrudes outward from said skirt.

3. The shadow mask recited in claim 2 wherein each of said ribs protrudes from said skirt at substantially a constant distance from an area adjacent the domeshaped face to the outer edge of said skirt.

4. The shadow mask recited in claim 2 wherein each of said ribs protrudes from said skirt at a distance which increases from an area adjacent the dome-shaped face to the outer edge of said skirt.

5. The shadow mask defined in claim 2 wherein each of said ribs has a substantially rectangular cross section.

6. The shadow mask defined in claim 2 wherein each of said ribs has a substantially triangular cross section.

7. The shadow mask defined in claim 2 wherein each of said ribs has a substantially semicircular cross section.

8. The shadow mask defined in claim 2 wherein each of said ribs becomes progressively larger with distance from an area adjacent the dome-shaped face. 

1. A shadow mask adapted to be mounted within a color television picture tube having a plurality of electron guns therein such that a Z axis extending between the center of the electron guns and the center of said mask is oriented normal to the plane of the incremental area of said mask wherE said axis intersects said mask, said mask comprising: a dome-shaped face; a skirt extending from the periphery of the dome-shaped face substantially parallel to said Z axis; and a plurality of ribs formed in said skirt, each of said ribs extending longitudinally along the general direction of the Z axis and extending away from said skirt by no more than 0.025 inch.
 2. The shadow mask recited in claim 1 wherein each of said ribs extends substantially parallel to said Z axis and protrudes outward from said skirt.
 3. The shadow mask recited in claim 2 wherein each of said ribs protrudes from said skirt at substantially a constant distance from an area adjacent the dome-shaped face to the outer edge of said skirt.
 4. The shadow mask recited in claim 2 wherein each of said ribs protrudes from said skirt at a distance which increases from an area adjacent the dome-shaped face to the outer edge of said skirt.
 5. The shadow mask defined in claim 2 wherein each of said ribs has a substantially rectangular cross section.
 6. The shadow mask defined in claim 2 wherein each of said ribs has a substantially triangular cross section.
 7. The shadow mask defined in claim 2 wherein each of said ribs has a substantially semicircular cross section.
 8. The shadow mask defined in claim 2 wherein each of said ribs becomes progressively larger with distance from an area adjacent the dome-shaped face. 